The present invention relates to an apparatus and method to achieve early intake valve closing to improve fuel economy and reduce undesirable emissions.
Historically, the performance of an internal combustion engine has been limited by fixed valve lift profiles, i.e., fixed timing of the opening and closing of the valves relative to the angular position of the engine crankshaft and fixed lift of the valves. However, modern internal combustion engines may utilize one of several methods and/or devices to vary the valve lift profile to, at least in part, control the flow of gas and/or air into and/or out of the engine cylinders. Modern internal combustion engines may utilize devices, such as, for example, variable valve actuating mechanisms, two-step cam profile switching mechanisms, and deactivation valve lifters to vary the amount by which the valves of an engine are lifted (i.e., opened). Furthermore, engines may utilize devices, such as variable valve actuating mechanisms and cam phasers, to vary the timing of the opening and/or closing of the engine valves relative to the angular position of the engine crankshaft.
Early intake valve closing (EIVC) is one way in which valve lift profiles are varied.
As the term itself implies, EIVC involves the early closing of the intake valves, i.e., the intake valves are closed at an advanced angle of the engine crankshaft relative to the crankshaft angle at which the intake valves are closed in a conventional/fixed valve lift profile. For example, in an engine having a fixed valve train the intake valves are closed when the angular position of the crankshaft is approximately 240xc2x0 (two hundred forty degrees) past top dead center (TDC). Whereas in an engine utilizing a conventional EIVC strategy, the closing of the intake valves typically occurs at approximately 120xc2x0 (one hundred twenty degrees) past TDC. Thus, a conventional EIVC strategy reduces the duration of time during which the intake valves are open by closing the intake valves early. However, the angular position of the crankshaft at which the intake valves are opened is approximately constant or fixed in a conventional EIVC strategy.
EIVC is typically utilized under light engine operating loads to reduce parasitic pumping losses. Parasitic pumping losses are reduced because the engine is operating in an unthrottled condition and the pressure drop across the intake valves is low as the pistons are moving at a relatively low velocity near TDC. Thus, thermal efficiency of the engine is improved. However, lower effective compression ratios and lower cylinder power and torque result from a conventional EIVC strategy, and inefficiencies in combustion result. Under heavy engine operating loads the losses in power and torque render the strategy undesirable.
Therefore, what is needed in the art is an EIVC apparatus and method that varies the timing of both the opening and closing of the intake valves.
Furthermore, what is needed in the art is an EIVC apparatus and method that varies the amount of lift and the timing of the opening and closing of the intake valves.
Moreover, what is needed in the art is an EIVC apparatus and method that achieves improvements in fuel economy and reduces the level of undesirable emissions.
The present invention provides an early intake valve closing method and apparatus.
The invention comprises, in one form thereof, a method for early intake valve closing in an internal combustion engine having a crankshaft and at least one exhaust valve, the crankshaft having a top dead center position and a bottom dead center position. The method includes the step of determining engine operating load conditions and parameters. One of a plurality of predetermined valve lift profiles, each of which correspond to a respective range of engine operating load conditions and parameters, is selected dependent at least in part upon the engine operating load conditions and parameters. The engine is commanded to operate the engine intake valves according to the selected one of the plurality of predetermined valve lift profiles to thereby optimize fuel economy and reduce emissions at light to moderate engine loads, to improve torque and power at relatively full engine loads, and improve cold start engine operation under cold start engine conditions.
An advantage of the present invention is that early intake valve closing is achieved with relative mechanical simplicity.
Another advantage of the present invention is EIVC is implemented in such a way as to achieve improved fuel economy and reduced levels of undesirable emissions.